Switching arrangement for electrical fuses

ABSTRACT

A reversible switching arrangement for a projectile capable of being detonated upon impact with a target on the one hand and at a predetermined distance from the target on the other hand. The arrangement comprises an hermetically sealed envelope adapted to be mounted at the nose of the projectile. The envelope comprises a nose and an abutting base section, that are rotated about the longitudinal axis of the projectile relative to each other to switch between the impact and the proximity fuse circuits.

nited States Patent [i 51 Nordgren [451 Feb. 26, 1974 SWITCHING ARRANGEMENT FOR ELECTRICAL FUSES [75] Inventor: Lennart .lohn Nordgren, Vallingby,

Sweden [73] Assignee: U.S. Philips Corporation, New

York, NY.

22 Filed: Jan. 7, 1972 211 Appl. No.: 216,064

[30] Foreign Application Priority Data Feb, 2, 1971 Sweden 1291/71 [52] US. Cl 102/70.2 R [51] Int. CL... F42c 11/00, F42c 13/00, F42c 19/06 [58] Field of Search 102/702 R [56] References Cited UNITED STATES PATENTS 2,974,597 3/1961 Hesson 102/702 R Hayden 102/70! R Rabinow 102/701 R Primary ExaminerBenjamin A. Borchelt Assistant ExaminerThomas H. Webb Attorney, Agent, or FirmFrank R. Trifari [5 7] ABSTRACT A reversible switching arrangement for a projectile capable of being detonated upon impact with a target on the one hand and at a predetermined distance from the target on the other hand. The arrangement comprises an hermetically sealed envelope adapted to be mounted at the nose of the projectile. The envelope comprises a nose and an abutting base section, that are rotated about the longitudinal axis of the projectile relative to each other to switch between the impact and the proximity fuse circuits.

9 Claims, 6 Drawing Figures PATENIED FEB2 6 I974 SHEET 1 BF 2 Fig.1

PATENTEDFEBZBW SHEET 2 (JP 2 SWITCHING ARRANGEMENT FOR ELECTRICAL FUSES The invention relates to an arrangement in an electrical fuse comprising an envelope adapted to be mounted at the nose of a projectile, which envelope comprises on the one hand a measuring device for measuring the distance to an object in the vicinity of the projectile and acting upon an electrical igniter for initiating burst at a certain distance from the object (proximity fuse function) and on the other hand an impact device comprising at least one impact contact adapted to initiate burst upon impact of the projectile against a target. Such a fuse with combined function has previously been proposed, in which previously proposed construction switching can be effected from proximity fuse function to impact fuse function by melting a fusible wire arranged within the fuse and influenced via contacts from the outside. This fuse can thus only assume two conditions. When the fusible wire is not melted the fuse will serve as proximity fuse, while when the wire is melted the fuse serves as impact fuse. Switching from proximity fuse function to impact fuse function is not reversible, because, when the wire has been melted, the opposite condition with non-melted wire cannot be regained.

The object of the present invention is to produce a fuse with essentially improved properties in comparison with previously proposed constructions, which has been achieved in that the envelope consists of two envelope parts which are rotatable relative to each other about the longitudinal axis of the projectile and interconnected via a step positioning and sealing device in such manner that the envelope parts can assume given mutual angular positions corresponding to the given positions in the step positioning device under hermetic closing of the space within the envelope parts relative to the space outside the envelope, the envelope parts being provided with cooperating contact means included in an electrical circuit comprising said measuring device and impact device for reversible switching between different proximity fuse functions and/or switching between proximity fuse function and impact fuse function with or without delay by rotating the envelope parts relative to each other.-

By utilizing the envelope itself as switch for switching between proximity fuse function and impact fuse function an easily acessible and reliable switch is obtained which in combination with a suitable shape of the electrical circuit in which the switch is included can be so adapted that it allows a rapid and reliable matching of the fuse to all possible firing conditions. A great advantage when utilizing the invention is that only one type of projectiles has to be stored. Switching to the required function is done immediately before firing when the actual kind of target is known. By the fact that the switching is reversible it is also possible to use projectiles remaining from a firing occasion at a later occasion, when they may immediately be adapted to be used for the new target after switching if necessary.

A difficulty in realizing the invention is to ensure by simple means reliable sealing between the space outside the envelope and the space within the mutually rotatable envelope parts in which the electrical circuits are situated. The seal must be effective during the very extended storing times under difficult conditions to which such projectiles may be exposed and therefore extremely high requirements are imposed upon the seal whilst at the same time the possibilities to rotate the parts for switching purposes must not be prevented. In a preferred embodiment the sealing device consists of two opposite sealing surfaces lying in a plane substantially perpendicular to the rotation axis with an intermediate flexible sealing ring, the parts being kept together by means of a spring device adapted to press the parts axially towards each other and the said positioning device being constructed so that upon rotation from one position to the next position the parts are displaced axially in direction from each other so that in an intermediate position the spring force wholly or largely is taken up by the positioning device, while in the locking positions an appreciable part of the spring force is taken up by the elastic sealing ring.

By this compulsory guidance of the envelope parts in axial direction the sealing ring will be unloaded during the switching, which makes that such switching will be possible in spite of extremely high sealing pressures in the locking positions. During the first and the last part of such a switching motion between two adjacent locking positions a certain deformation of the sealing ring will take place, which, if the sealing pressure were maintained at this high value during the whole motion, would make the switching impossible, because the sealing ring would either be damaged or the force required for the motion would be so large as to render switching impossible. Because the sealing ring is unloaded during switching any suitably high pressure can be applied on the ring in the locking positions. High pressure will give an effective seal without the need for a particularly accurate shape of the sealing surfaces or the sealing ring, which thus can cheaply be manufactured while it is not necessary to maintain a given spacing between the parts. For achieving distinct locking positions it is important that in the locking positions an appreciable portion of the spring force delivered by spring device should be taken up by the positioning device, and the total spring force must therefore be so large that it will give both the required sealing pressure and a sufficient locking pressure in the locking positions. The axial guidance must further be such that in the locking positions the spring force is divided in a desirable manner between the sealing ring and the positioning device.

Another problem arising in such a switching device with a rotary switch in which the rotation axis for the switch coincides with the rotation axis for the projectile in which the fuse is mounted, is due to the very high inertia forces which act upon the switch at the instant of firing. If the locking forces which normally keep the switch in the set position should not be sufficiently high the switch may be brought to another non-wanted position at the firing instant, so that the fuse will have an incorrect function. It may also occur in certain types of impact that the fuse is exposed to very large inertia forces at the instant of impact, which forces could set the switch to a unwanted position before an ignition pulse has been delivered. According to another feature of the invention this problem is solved in that the envelope parts cooperate with a locking device, which normally allows mutual rotation of the parts for switching purposes but which upon firing of the projectile is adapted to automatically become operative under the influence of the inertia forces produced at the firing instant and then locks the parts in the set position relative to each other.

The invention is illustrated in the accompanying drawings, in which FIG. 1 is a sectional view of a switching arrangement according to the invention,

FIG. 2 is a bottom plan view of the upper envelope part in the arrangement of FIG. 1,

FIG. 3 is a top plan view of the lower part of the arrangement of FIG. 1,

FIG. 4 shows schematically the electrical operation of the switch and an electrical circuit in which the switch is included,

FIG. 5 is a detail view of a suitable embodiment of the positioning device and FIG. 6 is a sectional view of a locking device which automatically locks the envelope parts in the switching arrangement of FIG. 1 at the firing instant.

Referring now to FIG. 1, the envelope of an electrical fuse consists of two parts, a nose part 1 and a base part 2, which are kept together by a holder ring 3. The nose part is at its rear end terminated by a projecting flange 4, against which a ring-shaped spring 5 bears. The spring 5 is undulated as seen from the side in FIG. 1 so that the spring in the non actuated condition has a larger extension in the axial direction than the thickness of the ring-shaped spring. The holder ring 3, which surrounds the rear portion of the nose part and the front portion of the base part, has an inwardly directly flange 6 so that a space is formed between the two flanges in which space the spring 5 is enclosed. At its lower part the holder ring 3 has an extended portion 7 which during assembly has been pressed under deformation into a cone-shaped recess 8 in the base part 2. Assembly is effected under strong compression of the spring 5 in the axial direction, so that the spring 5 after assembly will keep the two envelope parts pressed together in the axial direction via the holder ring 3.

The base part 2 has on its upper side facing the nose part 1 a ring-shaped recess 10 for a sealing ring 11. The sealing ring is compressed between the bottom 12 of the recess and the plane underside 13 of the nose part 1, which surfaces therefrom form sealing surfaces. Behind the recess 10 there is on the base part a ringshaped portion having radial indentations 14 evenly distributed round the circumference with intermediate ridges 15, as will be described in more detail hereinafter. The indentations 14 cooperate with projecting portions 16 on the bottom of the nose part 1 so that a positioning device for setting the parts 1, 2 in predetermined mutual angular positions is formed. The projecting portions on the bottom of the nose part can either be evenly distributed or according to FIG. 2 be arranged in groups each containing several, for example three, projections. Within that portion of the base part which forms the said positioning device there is finally a groove 17 in which runs a guide pin 18 projecting from the nose part 1. The groove 17 is provided with two stops 19, 20 for limiting the motion of the two rotatable envelope parts and only allowing a certain relative motion.

At the centre of the nose part 1 there is an insulating supporting plate 21 having conductive contact plates cooperating with resilient contacts projecting from the base part 2. The contact plates form together with the contacts a switching device for function switching of the fuse.

An example ofa practical embodiment of the switching arrangement is shown in FIG. 4 which also shows the electrical circuit in which the device is included. The supporting plate 21 has according to FIG. 4 a first group of contact plates comprising three plates 22, 23 and 23' co-operating with a resilient counter contact 24, and a second group of contact plates consisting of four plates 25, 26, 27 and 28 cooperating with a second resilient counter contact 29. Both resilient counter contacts are grounded and will thus produce grounding of that plate with which the respective resilient contact comes into contact in the various switching positions.

The contact plates are permanently connected to an electrical circuit which consists on the one hand of an impact fuse part, generally designated 30, and on the other hand of a proximity fuse part designated 31. Both the impact fuse part and the proximity fuse part act on a common electrical igniter 32 which on the passage of current will initiate burst.

The impact fuse part consists according to FIG. 4 of two impact contacts 35, 36 with associated capacitors 37, 38 and a charging circuit 39 for the capacitors. The impact contacts each consist of two fixed electrodes, of which one is grounded and the other leads to the respective capacitor, and of a movable contact means which normally is in contact with only one of the electrodes but which upon impact against a target is thrown forward and will connect the two electrodes to each other. The capacitors are normally charged through the charging circuit 39 but upon closing of the respective contact the capacitor will be discharged through the electrical igniter 32 one end of which is earthed, and as a result the electrical igniter will initiate burst. Of the impact contacts one (36) has greater sensitivity than the other, which may for example be achieved in that the more sensitive contact is nearer to the movable contact means.

The proximity fuse part consists of a I-IF-oscillator 40 with antenna 41 for transmitting a continuous HF- signal. The antenna also receives signals reflected from objects in the vicinity of the projectile. By combination of the generated signal and the received signal a periodic variation in the oscillation condition of the oscillator is produced, the so called Doppler signal, the frequency of which is proportional to the speed of the projectile with respect to the target and the amplitude of which depends upon the strength of the reflected signal. The Doppler signal is derived from the oscillator and applied through a voltage divider 42 to an amplifier 43 and from this to an igniter circuit 44. This circuit is connected to a capacitor 45 having its opposite plate connected to the electrical igniter 32. The capacitor is normally charged through a charging resistor 46. At the appearance of a Doppler signal of a certain strength as measured at the input of the ignition circuit 44 a thyristor situated at the output of the igniter circuit is fired, which thyristor when fired will connect the junction point of the capacitor 45 and the resistor 46 to ground, so that the capacitor 45 is discharged through the electrical igniter 32 which as a result will initiate burst.

The connection between the electrical circuit as described comprising on the one hand the impact fuse part 30 and on the other hand the proximity fuse part 31 and the switching arrangement consisting of the contact plates 22, 23, 25-28 and the resilient counter contacts 24 and 29 will follow from the subsequent description of the switching operation.

The insulating supporting plate 21 with contact plates 22, 23, 25-28 is rotatable in steps to six different angular positions relative to the resilient counter contacts 24 and 29 which contact can be regarded as fixed. The setting positions are designated I, II, S and III-V which are assumed to be marked on the envelope part in which the supporting plate 21 is mounted. On the opposite envelope part which thus supports the resilient counter contacts 24, 29 there is a mark 48. The set position is designated as that marking on said first envelope part which is opposite the mark 48.

In the position as shown the switching arrangement is set in position S. In this the said first resilient contact 24 is in contact with the contact plate 22 leading to the non-grounded end of the electrical igniter 32. Thus the electrical igniter in this position has both its ends grounded and the fuse is inactivated. The second resilient contact 29 is in contact with the contact plate 26 which is connected to the charging circuit for the two capacitors 37, 38 of the impact fuse device. None of the capacitors can therefore be charged. The position S is the transport position and is used at all occasions when the projectile is not immediately to be used.

Now if the supporting plate is rotated two steps in counter-clockwise direction to the position I the resilient contact 24 will come into con-tact with the contact plate 23. This plate is connected to the charging circuit for the capacitor 38 included in the circuit for the more sensitive impact contact 36. The capacitor 38 cannot be charged and the more sensitive impact contact is inactivated. However, second capacitor 37 of the impact fuse device is not influenced and hence the associated somewhat more insensitive impact contact 35 is effective. The second resilient contact 29 in this position is in contact with the contact plate 25 leading to the capacitor 45 in the proximity fuse part. The capacitor 45 cannot be charged and the proximity fuse part is inactivated. If the insulating supporting plate is rotated from position I one step in a clockwise direction to the position II, the contact 29 still engages the contact plate 25 and the proximity fuse part is thus inactivated, while the said first contact 24 will not engage any contact plate. Both capacitors in the impact fuse device can be charged and both impact contacts are inactive, and hence the more sensitive contact will determine the resulting sensitivity. The positions l and II are the positions for impact fuse function with normal sensitivity and high sensitivity, respectively.

Now if the plate 21 is rotated beyond the transporting position S to the position III the first resilient contact 24 will again be in conductive connection with the contact plate 23 via a plate 23', so that the more sensitive impact fuse contact 36 is inactivated (this is also valid for the positions IV and V as the plate 23' extends beyond these positions). In position III the second resilient contact 29 engages the plate 27. This plate is connected to a point in the voltage divider 42 for the Doppler signal, which, when grounded through the contact 29, will produce an essential voltage reduction of the Doppler signal. If the plate 21 is rotated further one step to the position IV, the contact 29 will engage the contact plate 28. This leads to another point in the voltage divider 42, which, when grounded through the contact 29, will produce a somewhat smaller voltage reduction of the Doppler signal as compared with the foregoing case. If the plate 21 is further rotated one step to the position V, the contact 29 will not engage any contact plate on the supporting plate, and hence the voltage divider 42 will produce a negligible voltage reduction of the Doppler signal. In the positions Ill-V thus both the proximity fuse part and the impact fuse part with normal sensitivity are effective, so that the fuse will serve as a proximity fuse with the impact fuse function as reserve function. Due to the switching to different voltage division ratios for the Doppler signal, initiation of burst will occur at different values of the Doppler signal as counted at the output of the HF- oscillator, involving different sensitivities of the proximity fuse, the position 11] representing proximity fuse function with low sensitivity and the positions IV, V representing proximity fuse function with intermediate and high sensitivity.

In FIG. 5 is shown a detail view of a suitable embodiment of the positioning and holding device. The device is shown in its stable position, i.e. the locking position with the projecting portions 16 on the nose part 1 in engagement with the indentations 14 in the base part. At switching to another position by mutual rotation of the parts 1 and 2 these parts will during the motion be urged apart a distance h in the axial direction as compared with the stationary position. The distance h is selected such that when the spacing between the parts 1 and 2 is greatest the sealing ring 11 is quite free. The sealing ring is so dimensioned that when the parts are pressed together as shown in the locking positions it will take up a portion of the spring force produced by the spring 5 but not the whole force. A large part of the spring force is taken up by the positioning device so that distinct locking positions are obtained. At switcing to a new position the sealing ring 11 will initially be slightly deformed, which deformation, however, will disappear when the ring is made free by the axial displacement. Likewise a certain deformation takes place when the sealing pressure is again built up on reaching of the new locking position. The given shapes of the indentations and projections which form the positioning and holding device with comparatively steep flanks on the guide surface in the vicinity of the locking positions and a flat guide surface along the main part of the motion will facilitate switching to a new position and will produce distinct locking positions. Both the indentations 14 and the projections 16 can be manufactured in a simple manner by stamping.

The angular stepwise positioning device can suitably be combined with a locking device which at firing is automatically made effective for locking the switch in the set position. As an example of such a locking device there is shown in FIG. 6 an arrangement 50 in which the pin 18 projecting from the nose part 1 and serving primarily to limit the rotational motion by cooperation with the stops 19 and 20 is adapted to simultaneously serve as a locking device after firing. The pin 18 is for this purpose displaceable within a sleeve 51 mounted in the nose part 1 with its opening from which the pin 18 projects facing the base part 2, i.e. directed backward as seen in the travelling direction of the projectile. The pin 18 is kept pressed into the sleeve by means of a compression spring 52 acting between two stop surfaces 53, 54 on the pin and the sleeve, respectively. In this position the pin 18 projects such a distance from the nose part 1 that it will engage the stops 19, 20 but will be free from the bottom of the groove 17. The spring force of the spring 52 is taken up by a pin 55 which is loosely arranged within the sleeve with one end situated in a recess 56 in the pin 18 and the opposite end introduced into a centrally situated aperture 57 in a bushing 58 arranged within the sleeve 51. Finally in the bottom of the groove 17 there is opposite the pin 18 in each of the positions it assumes in each of the setting positions I, II, III, IV and V (not the position S) a recess 59. The recesses 59 can suitably be made by stamping in the same manufacturing step as the stamping of the indentations 14 of the positioning and holding device (FIG. 3). In order to make the stamping possible the groove 17 is previously provided with a continuous cut 60 in its bottom, which cut is so wide that it can receive the material forced aside at the stamping but not so wide as to prevent it from forming a stop for the pin 18 at those places where there are no recesses 59.

The operation of the device is that the pin 18 normally assumes its intermost position shown by full lines in FIG. 6, in which the pin 18 is free from the bottom of the groove 17. The loosely arranged pin 55 is held in the position as shown by the compression spring 52. Switching may be effected as as desired by setting to the required position. After the setting has been made and the projectile is fired the pin 18 will at the firing instant be displaced backward as seen in the travelling direction (downward in the drawing) under the influence of the strong linear acceleration which occurs at this instant. The pin 55, which is also influenced by the linear acceleration, follows the pin 18 downward until its upper end is free from the bushing 58. Owing to the rotation produced simultaneously the upper free end of the pin 55 is now thrown outward against the inner surface of the sleeve 51, so that the pin 55 tilts and will assume an oblique position within the sleeve 51, as shown by dotted lines in FIG. 6. When the linear acceleration decreases the pin 18 may have a tendency to return to its inner position. The upper end of the tilted pin 55 will butt against the lower end surface of the bushing 58 so that return motion is prevented. The return motion is also made difficult in that the influence of the centrifugal force on the pin 18 will increase the friction between the pin and the inner surface of the sleeve 51. The pin 18 will thus be kept locked in its outer position, in which position its lower end projects into the recess 59, as shown by dotted lines in FIG. 6. Thus the nose part 51 is prevented from rotating with respect to the base part 2 and the switch will remain in the set position. The rotation continues during the whole trajectory of the projectile and the switch is locked both during the travel towards the target and during the impact against the target.

WHAT IS CLAIMED IS:

1. An adjustable electric fuse for use in connection with a projectile, including a plurality of electric ignitor circuits capable of being activated upon impact with a target and/or at predetermined distances from said target, comprising an envelope adapted to be mounted on said projectile, said envelope including a base section, a nose section arranged for rotation relative to said base section about the longitudinal axis of said projectile, sealing means disposed between said sections, holding means for resiliently urging said sections against said sealing means, positioning means coupled to said sections for retaining said nose section in selected angular positions relative to said base section and, respectively, for axially displacing said sections when rotated between said angular positions thereby relieving said sealing means, and switching means coupled to said sections for interconnecting said ignitor circuits according to a selected angular position of said sections thereby providing for reversible switching between said circuits.

2. An adjustable electric fuse as claimed in claim 1 wherein said holding means comprises a holder ring mechanically coupling said nose and base sections together and spring means cooperating with said holder ring and adapted to press said nose and base sections towards each other in the direction of the longitudinal axis of said projectile.

3. An adjustable electric fuse as claimed in claim 1, said sealing means comprising abutting surfaces of said nose and base sections, the surface of said base section proximate to the nose of said projectile having a recess, and a sealing ring positioned within said recess.

4. An adjustable electric fuse as claimed in claim 1 wherein said positioning means comprises a ring shaped portion of the surface of said base section proximate to the nose of said projectile having radial indentations with intermediate ridges around the circumference, and a projecting portion of the abutting surface of said nose section remote from the nose of said projectile cooperating with the ring shape portion of the abutting surface of said base section to angularly rotate said nose section relative to said base section.

5. An adjustable electric fuse as claimed in claim 4 wherein said positioning means further comprises the abutting surface of said base section having a circumferential groove adjacent the ring shape portion of the surface, stops projecting out of said groove at predetermined angular positions and a guide pin projecting from said nose section into said groove to limit the angular rotation of said nose section relative to said base section.

6. An adjustable electric fuse as claimed in claim 1 wherein said switching means comprises an insulating supporting plate member coupled to the nose section, a plurality of conductive sections, on said plate member providing connections to the impact and proximity fuse circuits in the nose and base sections of the envelope, and contacting members projecting from said base section to contact the conductive sections on said plate member thereby placing one of the impact or proximity fuse circuits in operating condition.

7. An adjustable electric fuse as claimed in claim 2 wherein said positioning means comprises intermediate and locking positions, the force of said spring means being wholly or substantially absorbed by said positioning means in said intermediate positions and being appreciably absorbed by said sealing means in the locking positions.

8. An adjustable electric fuse as claimed in claim 1 further comprising locking means cooperating with said positioning means to lock said nose and base sections under the influence of inertia forces thereby allowing rotation of said nose and base sections prior to firing of said projectile and preventing rotation of said nose and base sections upon firing of said projectile.

9. An adjustable electric fuse as claimed in claim 4 wherein said projecting portion of the abutting surface of said nose section remote from the nose of said projectile comprises a plurality of groups, each group comprising a plurality of individual projections. 

1. An adjustable electric fuse for use in connection with a projectile, including a plurality of electric ignitor circuits capable of being activated upon impact with a target and/or at predetermined distances from said target, comprising an envelope adapted to be mounted on said projectile, said envelope including a base section, a nose section arranged for rotation relative to said base section about the longitudinal axis of said projectile, sealing means disposed between said sections, holding means for resiliently urging said sections against said sealing means, positioning means coupled to said sections for retaining said nose section in selected angular positions relative to said base section and, respectively, for axially displacing said sections when rotated between said angular positions thereby relieving said sealing means, and switching means coupled to said sections for interconnecting said ignitor circuits according to a selected angular position of said sections thereby providing for reversible switching between said circuits.
 2. An adjustable electric fuse as claimed in claim 1 wherein said holding means comprises a holder ring mechanically coupling said nose and base sections together and spring means cooperating with said holder ring and adapted to press said nose and base sections towards each other in the direction of the longitudinal axis of said projectile.
 3. An adjustable electric fuse as claimed in claim 1, said sealing means comprising abutting surfaces of said nose and base sections, the surface of said base section proximate to the nose of said projectile having a recess, and a sealing ring positioned within said recess.
 4. An adjustable electric fuse as claimed in claim 1 wherein said positioning means comprises a ring shaped portion of the surface of said base section proximate to the nose of said projectile having radial indentations with intermediate ridges around the circumference, and a projecting portion of the abutting surface of said nose section remote from the nose of said projectile cooperating with the ring shape portion of the abutting surface of said base section to angularly rotate said nose section relative to said base section.
 5. An adjustable electric fuse as claimed in claim 4 wherein said positioning means further comprises the abutting surface of said base section having a circumferential groove adjacent the ring shape portion of the surface, stops projecting out of said groove at predetermined angular positions and a guide pin projecting from said nose section into said groove to limit the angular rotation of said nose section relative to said base section.
 6. An adjustable electric fuse as claimed in claim 1 wherein said switching means comprises an insulating supporting plate member coupled to the nose section, a plurality of conductive sections, on said plate member providing connections to the impact and proximity fuse circuits in the nose and base sections of the envelope, and contacting members projecting from said base section to contact the conductive sections on said plate member thereby placing one of the impact or proximity fuse circuits in operating condition.
 7. An adjustable electric fuse as claimed in claim 2 wherein said positioning means comprises intermediate and locking positions, the force of said spring means being wholly or substantially absorbed by said positioning means in said intermediate positions and being appreciably absorbed by said sealing means in the locking positions.
 8. An adjustable electric fuse as claimed in claim 1 further comprising locking means cooperating with said positioning means to lock said nose and base sections under the influence of inertia forces thereby allowing rotation of said nose and base sections prior to firing of said projectile and preventing rotation of said nose and base sections upon firing of said projectile.
 9. An adjustable electric fuse as claimed in claim 4 wherein said projecting portion of the abutting surface of said nose section remote from the nose of said projectile comprises a plurality of groups, each group comprising a plurality of individual projections. 